The question of which is better, soil or hydroponics, begins with an explanation of what each method entails. Many growers who believe they are growing in soil, are actually growing in a soilless growing mix.
Technically, soil is comprised of three particles; sand, silt, clay, as well as a sufficient amount of organic matter (see soil texture for more details). Potting soil, which contains very minute amounts of actual soil particles (if any at all), is instead comprised of aged and green organic matter, with varying amounts of perlite or vermiculite, and some added plant nutrients.
Many gardeners who grow in pots or raised beds are doing so in a potting soil grow media and would likely characterize it as growing in soil, not hydroponically, but it could technically be considered a gray area between the two growing techniques.
Before we begin comparing soil to hydroponics, it’s important to clarify just what is hydroponic and what is not. The decision breaks down to whether plants are being grown indoors or out. However, this classification misses many significant points. If based on the original idea of the absence of true soil particles, this would improperly group many techniques incorrectly.
One aspect of hydroponic growing that is commonly noted is the increased control over various aspects like temperature, nutrient concentration, and even root-zone oxygen. This can be accomplished inside a grow tent or many types of greenhouses, but not necessarily outdoors.
The variation of nutrient concentration can quickly be accomplished in Deep Water Culture (DWC), as compared with other grow medias. This is due to the residual nutrient level in media other than water, and any change in that level is stabilized. In DWC, the entire reservoir can be rapidly changed over and the resulting nutrient formula can be completely different.
Let’s compare DWC with old fashioned grow-in-the-dirt outdoor agriculture, which are probably the two extremes of hydroponic-versus-soil grow techniques. This dirt, we can assume, includes a good supply of organic matter in addition to the traditional soil particles.
Living Grow Media
With either of these two techniques, there are some very critical parameters that will determine plant taste and human nutrition quality, in addition to plant vigor and health. A “living soil” is essential to obtaining the best results from our soil garden.
The beneficial microbes, fungi, and bacteria that multiply and work in our garden are essential to plant nutritional uptake, and hence flavor, as well as nutritional output. The same is true of DWC—we need liquid nutrients continuously flowing past the root system to be alive with beneficial microbial life to assist in the development and uptake of vital plant nutrients.
Mycorrhizal fungi are an essential part of a root system’s ability to take up more nutrients from whatever grow media the roots live in. Bacteria are required to convert many nutrients into an available form.
With water culture, these fungi can be introduced but until they have attached to actual roots they do not increase in biomass. These microbes also require a consistent and adequate supply of available oxygen to survive. It does not take long for the vital microbial life to die off in the absence of oxygen.
Though flavor is, to a great degree, inescapably subjective, there is a science behind what impacts it. Tissue samplings can verify the nutritional content of a vegetable, removing the subjectivity aspect for the health aspect. Nutritional content within the plant root system will be directly related to the nutritional content of the plant tissue.
Soil vs. Hydroponics: Taste
If we are to review the “taste” aspect of the soil versus hydroponic question, we will need to look at just what makes the fruit or leaf of a garden crop taste good. What nutrients within a leaf, fruit, or root create the desirable flavors that most people want? We need to consider that the senses of taste and smell are subjective.
The primary flavor categories are: astringent, bitter, pungent, salty, sour, and sweet. The aspect of sweetness is easily measured within the roots or leaves of a plant. The rating factor for the level of these sugars, called brix, can be measured by a refractrometer.
Other aspects of flavor is pungency, or “hot and spicy.” With peppers this is a major point, and to measure this, we look at capsaicin content. For this factor, a high-performance liquid chromatography measurement is taken and rated in Scoville heat units (SHU).
Sour foods are generally acidic. This quality can be measured, but it’s tricky. Sour does have other chemical properties and some foods can be acidic because they are pungent.
Many people do not like to eat their vegetables—their phytonutrient content can make them bitter. These seem to have been produced by the plant through its evolution for self-protection. These phytonutrients are things like phenols, flavonoids, isoflavones, terpenes, glucosinolates, and other compounds that can help fight off cancer and produce positive health effects, but may not appeal to our sense of taste. Healthy plants produce more of these; this is what gives them the ability to fend off pests.
Because of this bitterness, many large food suppliers or growers have sought to breed a lower level of these nutrients into their crops to improve desirability and hence sales. Though calcium is vital for the health of plants and humans, its content in veggies has also been thought to increase bitterness. A reduction in the supply of calcium to a plant will reduce its calcium content and lower bitterness, but is it appropriate to reduce calcium?
Whether we realize it or not, the aspect of bitter within a vegetable adds to the overall richness and enjoyability of food and can balance out a dish that would otherwise be too sweet or salty.
What Types of Things Improve a Plant's Flavor?
The healthier a plant is, the more of its natural chemicals and flavors will be exhibited. To say one technique of growing (soil or hydro) produces a less-bitter flavor than another takes this issue in the wrong direction. Bottom line: to obtain the maximum flavor and the healthiest produce, it is important to obtain optimal plant vigor by providing all the necessary nutrients.
Using the same soil to grow the same crops year after year diminishes the productivity of the crop as well as its flavor. The major cause of this is depletion of essential micronutrients in the soil, as well as the likelihood that microbe variety and count may have diminished. Remember that the life within the grow media (presence of beneficial microbes) is key to plant nutrient uptake. Various bacteria and fungi need to work symbiotically with the plant roots to produce vigorous, healthy, and tasty produce.
Soil vs Hydroponics: System Comparisons
The microbiology within the grow media is just as important no matter which system (soil or water) we choose. Though DWC offers the opportunity to quickly measure and adjust the nutrient mix and microbial life forms, it also requires a continual awareness of what is going on within the media. A healthy living soil media is much slower to respond to any change you make; because of this, maintaining stability can be easier.
Controlling nutrient levels and media microbiology is the essence of producing optimum flavor and health benefits. Ambient air and media temperatures also contribute to these factors, and these aspects can be controlled better in hydroponics. In the correct season (provided local climate allows), soil grows will typically neutralize this benefit to a great degree.
Anecdotal reports on flavor or health benefits on each of these growing techniques will continue to be debated. (See the resources for this article for more details on the debate). As time and controlled studies continue there will exciting new things to learn. Current science would seem to indicate that either method can be used for optimal flavor and nutrition when operated properly.
Picking the technique that matches a particular grower’s needs seems to be the most important choice.
- How much time and expertise does the grower have available?
- Is the climate where the grower is located going to provide the necessary conditions for optimal plant health and vigor?
As for the possible conflict between providing optimal health or best flavor, it is the grower's decision, in addition to his or her subsequent efforts, that make the difference, not really which of these systems is used.